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Some Key points regarding Pneumocystis Jiroveci
- Previously it was called Pneumocystis carinii
- Thought to be a protozoan. Presently it is believed to be a fungus.
- But antifungal drugs are ineffective
- P. jiroveci is the only Pneumocystis species that infects humans,
- Pneumocystis jiroveci is common in the environment and does not cause illness in healthy people.
- Organism of low virulence
- Most 5 years old children in USA has antibodies to this organism
- Asymptomatic infection quiet common
- Pneumocystis jiroveci was a relatively rare infection before the AIDS epidemic
- In tissue it appears as cyst: That resemble the cyst of Protozoa.
- Does not grow in vitro in fungal culture media
- Requires tissue culture/cell lines for its growth and viability.
- Absence of ergosterol in cytoplasmsic membrance: insensitive to antifungal drugs
- Susceptible to selected anti-protozoan agents
- Pneumocystis takes fungal stain eg. Methenamine silver stain
- Possess chitin in all stages of its life cycle
- The protein synthesis elongation factor (EF3) and thymidylate synthase of Pneumocystis are more homologous to those of ascomycetous fungi
- Pneumocystis and fungi have similar cyst wall ultrastructure
- The ribosomal RNA studies reveal that 16S like RNA of Pneumocystis shares substantial sequence homology with various species of Ascomycota
Some points regarding pathogenesis of Pneumocystis Jiroveci
- Extracellular pathogen
- Transmission occurs by inhalation.
- Escape the defence of upper respiratory tract
- Deposition in alveoli
- Trophozoites attach to alveolar epithelium (alveolar type I epithelial cells) and proliferate
- Alevolar type II cell hypertrophy: Macrophage infiltrate and filling
of alveolar spaces with foamy eosinophilic material and plasma cells.
- Plasma cell pneumonia
- Foci of necrosis and cellular debris in extrapulmonary sites.
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